HELP!!!!
there's a blizzard forecasted 4 days from now, and suddenly my plow truck (combination of an 82 f-100, an 86 f-250, and an 89 f-150 put together) started knocking really bad. the engine is out of a 86 f-250 and its the 300 six cylinder. the engine started tapping at first while driving, then i pulled over and it started knocking really bad. i assumed it was low on oil so i added some oil and attemped to start it again. it kept knocking just as loud. keep in mind that the whole time this was happening the oil pressure gauge read normal pressure. it sounded like either a rod or crank bearing had gone bad, and it was running rough and lost alot of power as i was attempting to get it off the roadway. so now i'm thinking of where i'll find another bottom end and have it in the truck within 4 days. i had my brother drive me home and get my other truck... when i came back to the plow truck to get some stuff out of it i started it back up to see if it still knocked. to my surprise it didn't? it ran just fine and didn't knock a bit. i thought for sure that i had spun or lost a bearing before but now i'm not sure. i tried to drive the truck home but notice the faint knock slowly coming back so i cut it back off and left it for the night.
has anyone ever had this problem before? the engine only has 100k on it. i think i'm just gonna take the pan off tomorrow and replace the oil pump and screen. would that just be a waste of money? could a bearing still be bad? i'm trying to get the truck running again before the snow gets here. if anyone has any input please help me i'm running out of time!!

 

Check the timing gear ( cam gear ) I had this very same thing happen and it turned out to be the cam gear had chiped a couple if teeth off and it sounded like a rod knocking. It was one of those fiber type gears.

 

I had a similar thing happen on a 56 Dodge, after I opened it up on a straightaway to blow it out on my way home one night.

Turned out to be sludge in the crankcase, stirred up & clogging the oil pump screen, but on drain down overnight, the knock was gone & oil prssure was fine on the start the next morning.

I flushed the oil pan out with varsol & got loads of gunk out from deposits remaining from the 30wt Wolfs Head motor oil that the previous owner had been running in it.

SO, if the cam gear isn't at fault & you think you might have a sludged up oil sump that's clogging the oil pump screen, maybe consider dropping the pan & have a look.

 

If you have low, but not zero, oil pressure, the "fake" oil pressure gauge on the dash (post -'86 Fords) will read normal. So, you dont really have early warning of wear. Put in a cheap mechanical gauge before you open up the engine.

If it is a cam gear problem, I dont know how hard it is to change a gear, not chain, timing set on a 300. A few applications (non-Ford) that I know require camshaft removal due to the pressed on or riveted cam gear. Hopefully, if that is the problem, Fords are bolted on.

Jim